1. Field of the Invention
The present invention relates to an image display apparatus for displaying an X-ray digital image as a typical radiation diagnosis image and, more particularly, to an image display apparatus for displaying an image to guide a catheter to a target portion of an object to be examined so as to perform radiation diagnosis.
2. Description of the Related Art
In an X-ray angiographic system, such as a typical conventional image display system for radiation diagnosis, intervention radiology is utilized. In this intervention radiology, a catheter is percutaneously injected into a patient and is guided to a morbid portion, and medicine is injected into the morbid portion through the catheter.
An application of intervention radiology to an X-ray diagnostic apparatus will be described below. X-rays emitted from an X-ray tube are transmitted through the object, and the transmitted X-rays are detected and converted into an optical image by an image intensifier. This optical image is converted into a TV video signal by a TV camera through a lens system. The TV video signal is input to a TV monitor. A fluoroscopic image of a bone portion and the like of the object is displayed on the TV monitor.
In this X-ray fluoroscopic state, an operator inserts a catheter and a guide wire into a blood vessel of the patient. The following operations have been desired. The operator can confirm the position of the catheter while observing the fluoroscopic image displayed on the TV monitor. The operator can inject the catheter into the blood vessel while manipulating the guide wire, so that the catheter can be guided to a target portion.
However, when the thickness of the object is large, the amount of X-rays transmitted through the object is small and sand-like photon noise is generated. In addition, the amount of X-rays emitted from the X-ray tube is not uniform, and the sand-like photon noise is generated when the amount of X-rays emitted from the X-ray tube is not uniform. Since the photon noise is present in the fluoroscopic image when the amount of X-rays transmitted through the object is small, the guide wire and the catheter cannot be easily observed. For this reason, the operator can not see the guide direction of the catheter inside the blood vessel when the photon noise is present. It is thus difficult for the operator to insert the catheter inside the blood vessel. If the amount of X-rays transmitted through the object is increased by an increase in voltage applied to the X-ray tube, the ratio of signal components of the fluoroscopic image to photon noise is increased to allow the operator to easily observe the guide wire and the catheter. However, if the dose of the X-rays irradiated onto the patient is increased, the patient may be adversely affected by the large amount of X-rays.